Invincibility
While playing the game, press Back to display the objectives window, then quickly press Down, Up, Down(2), Up, Right, Left, Right, Y, X(2), A. Your health will still decrease, but will never reach zero.

Full ammo for all weapons
While playing the game, press Back to display the objectives window, then quickly press B, A, X, Y, Left, Right, Left.

Full health
While playing the game, press Back to display the objectives window, then quickly press B, A, B, A, Up(2), Down, X.

Get all
While playing the game, press Back to display the objectives window, then quickly press Up(2), Down(2), Left, Right, Left, Right, B, A.

Multiplayer ranks and awards
Complete the indicated tasks to unlock the corresponding rank or award in Multiplayer mode:

Basic Training: Play over 100 ranked matches.
Bronze Flag: Get over 100 flag captures in ranked matches.
Combat Veteran: Play over 1,000 ranked matches.
Corporal (Multiplayer): Get over 500 win points in ranked matches.
Private (Multiplayer): Get over 100 win points in ranked matches.
Lieutenant (Multiplayer): Get over 1,000 win points in ranked matches.
First Tour Of Duty: Play over 500 ranked matches.
General (Multiplayer): Get over 5,000 win points in ranked matches.
Gold Flag: Get over 1,000 flag captures in ranked matches.
Guts But No Glory: Get over 100 Assists in ranked matches.
Number One: Get number 1 on the Leaderboards.
Perfect Win: Win a ranked match without being fragged.
Raven Squad: Get over 5,000 frags in ranked matches.
Rhino Squad: Get over 10,000 frags in ranked matches.
Seasoned Warrior: Play over 1,0000 ranked matches.
Silver Flag: Get over 500 flag captures in ranked matches.
The Best Impression: Get over 250 Impressive medals in ranked matches.
The Defender: Get over 250 Defense awards in ranked matches.
The Golden Gauntlet: Get over 250 gauntlet frags.
Top Ten: Get a top 10 rank on the Leaderboards.
Viper Squad: Get over 100 frags in ranked matches.
Warthog Squad: Get over 500 frags in ranked matches.
Your Excellency: Get over 500 Excellents in ranked matches.

Single Player ranks and awards
Complete the indicated tasks to unlock the corresponding rank or award in Single Player mode:

Ballistics Expert: Complete a level using only the rocket launcher.
Blaster Master: Complete a level using only the blaster.
Blazing Buckshot: Complete a level using only the shotgun.
Corporal (Act 1 ): Complete Act 1 with the rank of Corporal.
Corporal (Act 2 ): Complete Acts 1 and 2 with the rank of Corporal.
Corporal (Defeated The Strogg ): Complete the game with the rank of Corporal.
Enlightening: Complete a level using only the lightning gun.
Full Arsenal: Complete a level where a shot with every weapon hits.
Galactic Order of Heroism: Fight alongside Raven Squad.
General (Act 1 ): Complete Act 1 with the rank of General.
General (Act 2 ): Complete Acts 1 and 2 with the rank of General.
General (Defeated The Strogg ): Complete the game with the rank of General.
Hyperactive: Complete a level using only the hyperblaster.
Lieutenant (Act 1 ): Complete Act 1 with the rank of Lieutenant.
Lieutenant (Act 2 ): Complete Acts 1 and 2 with the rank of Lieutenant.
Lieutenant (Defeated The Strogg ): Complete Acts 1 and 2 with the rank of Lieutenant.
Pineapple King: Complete a level using only the grenade launcher.
Private (Act 1 ): Complete Act 1 with the rank of Private.
Private (Act 2 ): Complete Acts 1 and 2 with the rank of Private.
Private (Defeated the Strogg ): Complete the game with the rank of Private.
Solar Star of Courage: Fight alongside Viper Squad (Hangar2).
Sky Marshall's Medal of Valor: Rescuing Pvt. Lanier of Eagle Squad (Waste).
The Machine: Complete a level using only the machine gun.
Tooth and Nail: Complete a level using only the nailgun.
The Dark Lord: Complete a level using only the DMG.
The Sniper: Complete a level using only the railgun.
Untouchable: Complete a level without taking damage.

Fast Weapon Achievement
After you finish with the last tower (the Data Processing Security tower) go to lift just right before the level exit and save the game. Keep this save game alive so you can farm this file.

Pick a weapon in your inventory and exit the level. Upon loading the next map, do not change your weapon and proceed to kill the big monkey strogg enemy before you approach the tram and exit this map.

Simply reload the save game from the Data Processing Security tower and repeat the tram map with each weapon and you'll bag all the achievements quickly.